It is proposed to use phospholipid vesicles as carriers for introducing several chemotherapeutic agents into tumor cells, both in vitro and in vivo (mice). Several types of vesicles will be used of varying physical and chemical properties. Study will be done for maximal incorporation of the drugs into vesicles, characterization of their uptake by tumor cells in vitro and assay of their biological effects, study of the rate of clearance in vivo of vesicles plus drug from blood, tissue distribution and anti-tumor effects. BIBLIOGRAPHIC REFERENCES: Papahadjopoulos, D., Poste, G., Vail, W.J. and Biedler, J.L. "Use of Lipid Vesicles as Carriers to Introduce Actinomycin D into Resistant Tumor Cells" Cancer Research 36: 2988-2994, 1976. Poste, G. and Papahadjopoulos, D. "Drug Containing Lipid Vesicles Render Drug Resistant Tumor Cells Sensitive to Actinomycin D" Nature, 261, 699-701, 1976.